Electrical – Dash and Running Lights Not Working

What this Article Covers

Issues with the dash, climate control, and running lights not functioning.

Issue Symptoms

The instrument panel (dash) lights fluctuate between being bright and dim, and sometimes completely shut off.

When both the dash and climate control lights turn off the running lights (amber side lights and rear tail lights) also shut off.

If the light switch is set to the Head position only the headlights came on, all other lights turn off.

My Backstory

I had an issue with my instrument panel lights that progressively got worse over a few months. At first my dash lights would just get dim and then go back to full brightness randomly; but as time went on, the dash, climate control, and running lights would all shut off together while driving.

There appeared to be no rhyme or reason as to why the issue was occurring. The only semi-helpful thing was that I could do was smack and toggle the light switch to get the lights back on for a little while, but the issue would come back and my lights would go out while I was driving.

Here’s an example of what was occurring to me:

Troubleshooting

There are a wide range of reasons for issues with the instrument panel and running lights to occur (they are all on the same electrical circuit). The following troubleshooting steps will give you a good opportunity to narrow down what is causing your particular issue to occur.

Recommended Tools

Toyota Service Manual (aka the “Big Green Book”)

Flashlight

Phillips Head Screwdriver

10mm Socket

Multi-Meter

Spare Wire

Crimps or Solder

Lots of Patience

Steps to Take

1. Check Fuses

Generally a blown fuse shouldn’t happen unless there is something seriously wrong but occassionally a fuse blows due to a random occurrence. When checking fuses use a continuity test with a multi-meter — as a visual inspection can sometimes miss hairline breaks in the fuse. If there is any doubt you can also just replace the fuses with brand new ones. Here are the ones I recommend checking / replacing:

Junction Box No. 5 (Engine Bay)

50 amp AM1

60 amp HEAD

7.5 amp AM2

10 amp HAZ-RADIO

Relay Box No. 1 (Driver’s Side Foot Panel)

15 amp TAIL

7.5 amp DOME

15 amp STOP

7.5 amp TURN GAG

15 amp RAD CIG

2. Check the Light Switch

Toggle the Light Switch: Toggle the light switch between an off state (either the Off position or the Hold position) and an on state (either the Tail position or Head position). This can help determine if they light switch’s contacts are going bad — especially if the lights come on when the switch is half-way between two settings.

Check / Bypass the Dimmer Switch: The dimmer switch has been known for cracking and causing the lights to stop working. This can be tested by seeing if you can spin the dimmer switch all the way around freely. If the dimmer switch stops at a certain point going up or down your dimmer switch should be working correctly. However, you can always bypass the dimmer switch if you have no need for it by soldering on a new wire between the two contact points, or by connecting a temporary jumper cable (the ones with the little alligator clips on the ends used for breadboard testing circuits).

Clean the Light Switch: Remove the light switch, open it up, and clean the contact points that the switch presses when being rotated. Sometimes this contact area gets dirty or corroded and blocks the connection in certain spots.

Light Switch Contact Points

Re-solder the Light Switch Contacts: The solder points on the light switch can go bad over the years of being heated up, cooled down, and vibrating. Re-soldering all of the solder points is a good idea to ensure there are no microscopic tears in the solder.

Light Switch Circuit Board

3. Check the Instrument Panel

Verify the Dash Lights Work: Remove the instrument panel and connect an appropriate 12 Volt battery to the Illumination (ILM+, ILM-) contact points for the dash lights. If the lights don’t come on then it’s likely that the light bulbs are bad or there is a break somewhere in the circuit on the instrument panel. (See this related article for more details on working with the dash lights).

4. Check the Junction Boxes and Wires

Check the No. 3 Junction Box: There is a junction box in the corner of the driver’s side foot-well to the left of the clutch pedal. Try unplugging the connector for the dash lights and then re-connecting it.

Check the Wires in the Circuit: With the light switch in an ‘on’ state, try jiggling and bending the cables going to the junction box to see if the lights come on. If this ends up being the issue you can replace the wires, or just zip-tie them in place to maintain a connection temporarily.

See my video for an example:

Re-solder the Junction Box: Just like the light switch, this junction box’s soldered connections sometimes crack over time. I recommend taking the junction box out (be careful with removing the ribbon cable) and re-soldering all points on it.

5. Bypass the Junction Boxes and Wires

Cut Out and Remove Junction Box 3 and 4: These two junction boxes are linked by a blue ribbon cable, and run from the driver’s side footwell to the passenger’s side footwell.

In my particular case, this is what I had to do to ultimately fix my issues. Junction box 3 had microscopic cracks in the circuit board, which resulted in me constantly having issues with my lights dimming or shutting off randomly.

Here is a color coded diagram that I made of these two junction boxes and how they are connected by the ribbon cable (the little cluster in the top left of each image):

Junction Box 3 and 4 – Color Coded Wiring Diagram

Note: The above image was created in MS Paint after hours of using a multimeter while crawling under a dash. Download it and zoom in if you need to to see the stripe color on some wires.

Using this diagram I made (as well as several wing nuts, heat shrink, electrical tape, zip ties, and lots of wire) I was able to bypass the junction boxes and successfully resolve my issue.

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6 comments

Hi,
Excellent write up. My dash lights went dark after R&R dash. I didn’t do the pull or put back so mostly clueless here. My SW20 has plugs into back of various dash pieces. Running, tail, brake and signal lights are fine (I hope). Do you know of any info pages referring to SW20 that cover the same info? I got mine a month or so back and am in process for title from salvage to rebuild or whatever California calls it. Personally don’t care as long as the frame and suspension are solid. They seem to be. :)) No unexplained movements on 10 mile or so very twisty country roads to/from my place. Read that the MR2 is “first car that puts a smile on my face every time I start it,” and figured you might appreciate the sentiment.

I don’t have anything on the SW20 currently, but I’m sure the SW20 Facebook groups will probably have more than enough info on their more modern electrics lol. For the most part, everything can be solved by tracing the wires with a multimeter — checking where the power is and where it stops.

I agree with you on the salvage title. If the frame and suspension are good, you should be in fine shape. I’d just make sure to keep it as a projects car, since even a rebuilt title depreciates the value by a lot if you ever go to sell. My AW11 has a clean title, but it will probably stick around until it falls apart lol.

This weekend I’m actually going to be replacing the cracked exhaust manifold and hopefully be driving it again. I have a lot of articles I still need to post, just haven’t had much time for it between work and other responsibilities. As soon as I get some more time though I’ll be overhauling this website and posting all of the articles I wanted to write.

Good luck with your SW20! And yes, I do appreciate the sentiment =D. I still love my car, even if it drives me nuts sometimes lol